Expandable metal membrane with orthogonally isotropic behavior

ABSTRACT

In a metal membrane for a low-temperature-fluid storage tank wherein longitudinal and transverse corrugations are formed and both corrugations intersect each other, a bidirectional expandable member connected to each corrugation is formed in the intersection of the corrugations so that the bidirectional expandable member is longitudinally and transversely expandable. The bidirectional expandable member is protruded and is shaped like a pyramid, a dome or a cross. Each metal membrane is welded into a unit panel and the edge of each metal membrane is welded with the common edge of another adjacent metal membrane.

PRIORITY CLAIM

This application is a continuation and claims the benefit of priority under 35 U.S.C. §§120, 365, and 371 to Patent Cooperation Treaty Patent Application No. PCT/KR2009/001946, filed on Apr. 15, 2009. This application further claims the benefit of priority to Korean Application No. 10-2008-0036754, filed Apr. 21, 2008. The disclosures of the above applications are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to a metal membrane with orthogonally isotropic behavior having corrugations to be expandable and thus suitable for storing cryogenic fluids such as liquefied natural gas.

BACKGROUND

Liquefied natural gas (“LNG”) is generally a cryogenic liquid having a boiling point of approximately −162° C. under atmospheric pressure and stored in a multiple structured storage tank for thermal isolation.

This LNG storage tank has a metal membrane inner tank and a thermal isolation layer surrounding the inner tank to store ultra-low-temperature LNG safely by preventing the loss of evaporation.

Since metal membranes are in direct contact with the ultra-low-temperature LNG, they must be made of metallic materials having excellent resistance to brittle fracture in a low temperature to respond against stress changes and have structure to facilitate expansion and contraction in response to heat and load. Each metal membrane is thus welded with the common edge of another adjacent metal membrane to keep a cargo air-tight.

Conventional metal membranes of a LNG storage tank are described below.

FIG. 1 and FIG. 2 are perspective views illustrating metal membranes of a LNG storage tank according to a conventional embodiment. U.S. Pat. No. 3,118,523 discloses “connecting element for expansion joints” in which corrugations 1, 2 of a metal sheet are connected with a top or cap portion 3 of square form at the intersection of two corrugations.

FIG. 3 is a perspective view illustrating a metal membrane of a LNG storage tank according to another conventional embodiment. U.S. Pat. No. 3,302,359 discloses “corrugated sheet-like yieldable wall element and vessels or tanks made thereof” in which an intersection area 203 is formed at the intersection of corrugations 202 a, 202 b of a metal sheet 201.

FIG. 4 is a perspective view illustrating a metal membrane of a LNG storage tank according to further another conventional embodiment. As shown in FIG. 4, a metal membrane 10 of a LNG storage tank has longitudinal and transverse expandable corrugations 11, 12 not to cause thermal stress due to extreme thermal deviation of about 200° C.

In addition to the metal membranes of a LNG storage tank described above, expandable metal membranes have been developed mainly for thermal isolation tanks of LNG carrier. JP Patent No. Sho 50-21008 discloses a membrane having Y-shaped intersection in which repeating hexagonal corrugations are formed with 120° . JP Patent No. Sho 60-14959 discloses a membrane having triangular corrugations and trapezoid corrugations crossing to the triangular corrugations. JP Patent No. Sho 60-32079 discloses a membrane expansion structure in which corrugations protruded on the surface are divergently arranged from at least one concentration section.

Further, KR Patent Application No. 1994-11802 discloses “membrane structure for LNG storage tank and method for manufacturing the same” in which the membrane structure includes 4 corrugations forming a cross shape and a ring knot. KR Patent Application No. 1994-11804 discloses “membrane structure for LNG storage tank” including four legs each of which includes a cross-sectioned insulating corrugation portion, a body portion having indented joints, an expanded portion indented towards the board member from an end portion of the body portion, and a valley portion.

In addition, various metal membranes have been disclosed in KR Patent Application No. 2003-83849 titled “Membrane Metal Panel of Insulated Cargo Tanks of LNG Carrier”, KR Patent Application No. 2003-83850 titled “Membrane Metal Panel of Insulated Cargo Tanks of LNG Carrier”, KR Patent Application No. 2003-92250 titled “Membrane Metal Panel of Liquefied Natural Gas Storage Tanks”, KR Patent Application No. 2004-6648 titled “Membrane Metal Panel With Flat Welding Joint Part for Insulated Cargo Tank of LNG Carrier”, KR Patent Application No. 2004-9306 titled “Membrane Metal Panel of an Insulated Cargo Tank Storing a Low Temperature Liquid That Has Flat Welding Joint”, KR Patent Application No. 2004-21526 titled “Membrane Metal Panel of LNG Storage Tanks”, and U.S. Pat. No. 3,324,621 titled “Cold Liquid Container and Elements for Use in Same”.

As described above, the metal membrane of a LNG storage tank according to a conventional embodiment in FIG. 4 has different height of each intersection where corrugations intersect each other. Plane rigidity in the longitudinal direction is thus 2 or more times higher than that in the transverse direction due to asymmetric shape at the intersections, which further causes different thermal stress according to the direction at a low temperature. Because the height of the corrugations in the transverse direction is relatively higher than that in the longitudinal direction at the intersection, they are expected to collapse easily for pressure such as sloshing and the like.

The plane rigidity of a metal membrane is influenced by the rigidity of bidirectional bent intersections rather than shape of corrugations themselves. Even though since height and width of transverse direction corrugations are higher, plane rigidity in the longitudinal direction should be less than that in the transverse direction in rigidity of conventional metal membranes according to the direction, plane rigidity in the transverse direction is less. This is caused by the shape of intersections of the conventional metal membrane since more corrugations in the cross direction to transverse direction corrugations are formed. A problem, that thermal stress of a metal membrane in the transverse direction is thus significantly higher than that in the longitudinal direction during contraction at a low temperature, is created.

The conventional inventions, including the inventions as described in FIG. 1, FIG. 2 and FIG. 3, have tried to obtain a symmetric shape in cross-directions or simplify welding lines to resolve such problems. However, the problem of the plane rigidity, which influences degree of thermal stress at an ultra low temperature, has not been solved. There has been no introduction of intersection structures efficiently expandable bidirectionally to reduce the plane rigidity. Therefore, even though corrugations are formed, it may not reduce the plane rigidity but cause significant thermal stress if straight lines connecting both corners of a unit panel along the surface of corrugations are formed or if straight welding joint is formed.

Since there is no membrane structure clamping using a clamping unit of an automatic welding robot, which is a major consideration in manufacturing a storage tank using a metal membrane as shown in FIG. 1, FIG. 2 and FIG. 3, problems are still when applied in actual field.

The present invention is therefore provided to resolve such problems as described above.

SUMMARY

An aspect of the present invention is to provide an expandable metal membrane having orthogonally isotropic behavior in a metal membrane of a low-temperature-fluid storage tank having longitudinal and transverse corrugations which intersect each other, wherein a bidirectional expandable member connected to each corrugation is formed so that the bidirectional expandable member is longitudinally and transversely expandable in the intersection of the corrugations, the bidirectional expandable member is protruded in a pyramid shape, and first caved grooves are formed at corners where lateral faces of the bidirectional expandable member are connected, second caved grooves are formed on a top part of the portion connected with the bidirectional expandable member in the corrugations, and clamping parts protruded to be clamped by a clamping unit are formed at both ends of the corrugations connected to the bidirectional expandable member.

Another aspect of the present invention is to provide an expandable metal membrane having orthogonally isotropic behavior in a metal membrane of a low-temperature-fluid storage tank having longitudinal and transverse corrugations which intersect each other, wherein a bidirectional expandable member connected to each corrugation is formed so that the bidirectional expandable member is longitudinally and transversely expandable in the intersection of the corrugations, the bidirectional expandable member is protruded in a dome shape, a neck part is formed at the portion where the bidirectional expandable member is connected in the corrugations, and clamping parts indented to be clamped by a clamping unit are disposed at either sides of the bidirectional expandable member between portions where the bidirectional expandable member and the corrugation are connected.

Still another aspect of the present invention is to provide an expandable metal membrane having orthogonally isotropic behavior in a metal membrane of a low-temperature-fluid storage tank having longitudinal and transverse corrugations which intersect each other, wherein a bidirectional expandable member, protruded in a cross shape and connected to each corrugation between branching parts of the cross shape, is formed so that the bidirectional expandable member is longitudinally and transversely expandable at an intersection of the corrugations, and clamping parts are formed in such a way that the clamping parts are clamped by a clamping unit at either lateral face of the branching parts by having the bidirectional expandable member protrude over the corrugations.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 and FIG. 2 are perspective views illustrating metal membranes of a LNG storage tank according to an embodiment of the conventional arts.

FIG. 3 is a perspective view illustrating a metal membrane of a LNG storage tank according to an embodiment of the conventional arts.

FIG. 4 is a perspective view illustrating a metal membrane of a LNG storage tank according to another embodiment of the conventional arts.

FIG. 5 is a perspective view illustrating a metal membrane of a LNG storage tank according to a first embodiment of the present invention.

FIG. 6 is a partially magnified sectional view illustrating an expandable metal membrane with orthogonally isotropic behavior according to a first embodiment of the present invention.

FIG. 7 illustrates a clamping part of an expandable metal membrane with orthogonally isotropic behavior according to a first embodiment of the present invention.

FIG. 8 is a perspective view illustrating an expandable metal membrane with orthogonally isotropic behavior according to a second embodiment of the present invention.

FIG. 9 is a partially magnified sectional view illustrating an expandable metal membrane with orthogonally isotropic behavior according to a second embodiment of the present invention.

FIG. 10 is a perspective view illustrating an expandable metal membrane with orthogonally isotropic behavior according to a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Bent intersections determining the plane rigidity of a metal membrane may be shaped like a pyramid, a dome or a cross to reduce plane rigidity and, at the same time, equalize plane rigidity of two intersecting directions so the metal membrane is easily clamped by a clamping unit of a welding robot or a transfer device.

Hereinafter, certain embodiments of the present invention will be described in detail with reference to the accompanying drawings. Throughout the description of the present invention, when describing a certain technology is determined to evade the point of the present invention, the pertinent detailed description will be omitted.

FIG. 5 is a perspective view illustrating a metal membrane of a LNG storage tank according to a first embodiment of the present invention and FIG. 6 is a partially magnified sectional view illustrating an expandable metal membrane with orthogonally isotropic behavior according to a first embodiment of the present invention. As shown in FIGS. 5 and 6, an expandable metal membrane with orthogonally isotropic behavior 100 according to a first embodiment includes corrugations 120 and 130, formed in the longitudinal direction and the transverse direction and intersecting each other, on a panel 110 made of metal, and a bidirectional expandable member 140 at the intersection of the corrugations 120 and 130, in which the bidirectional expandable member 140 is protruded and has a pyramid shape.

The corrugations 120 and 130 includes a first corrugation 120 and a second corrugation 130 whose cross sections form a fillet with the flat part and intersect each other on the panel 110, preferably orthogonally.

A plurality of the first corrugations 120 are formed to be parallel with each other in the longitudinal direction on the panel 110 so that they are expandable in the transverse direction of the panel 110.

A plurality of the second corrugations 130 are formed to be parallel with each other in the transverse direction on the panel 110 so that they are expandable in the longitudinal direction of the panel 110.

The bidirectional expandable member 140 is connected to each of the front and back and the left and right of the first and the second corrugations 120 and 130 at the intersection of the first and the second corrugations 120 and 130. Four (4) sides 141 having a pyramid shape are protruded upward like the first and the second corrugations 120 and 130, and are connected to each of the first and the second corrugations 120 and 130. The bidirectional expandable member 140 is thus able to let the corrugations be longitudinally and transversely expandable by changing the pyramid shape.

The bidirectional expandable member 140 includes first caved grooves 142 to provide expandability to the corners where the sides 141 are connected.

The first groove 142 may be clamped by a clamping unit of a welding robot instead of a clamping part 150 which will be described later, or a clamping unit of a transfer device which moves the metal membrane 100 along a guide rail.

The corrugations 120 and 130 include second caved grooves 121 and 131, respectively, to provide expandability to the top part of the portion connected with the bidirectional expandable member 140.

The bidirectional expandable member 140 may include the clamping part 150 to couple a clamping unit of a welding robot or a clamping unit of a guide rail to the membrane.

The clamping part 150 is formed to be protruded at both ends of the corrugations 120 and 130 to which the bidirectional expandable member 140 is connected to be clamped by a clamping unit. As shown in FIG. 5, the clamping unit is provided to be clamped in the “A” and “B” directions.

The upper part of the clamping part 150 is more protruded than the bottom part to prevent a breakaway when a clamping unit is clamped as shown in FIG. 7.

The expandable metal membrane with orthogonally isotropic behavior 100 according to a first embodiment of the present invention allows longitudinal and transverse expansion at intersection of the corrugations 120 and 130 by providing the expandable pyramid-shaped bidirectional expandable member 140 at the intersection of the corrugations 120 and 130 so that it reduces plane rigidity throughout the panel 110. Expandability in the longitudinal direction and the transverse direction of the panel 110 is kept by connecting the corrugations 120 and 130 to the bidirectional expandable member 140 to maintain continuity. Expandability is even improved and plane rigidity is significantly reduced by providing the first grooves 121 and 131 each formed at the first and the second corrugations 120 and 130, respectively, and the second grooves 142 formed at the bidirectional expandable member 140.

Further, a clamping unit of a welding robot or a transfer device may clamp the clamping part 150, which are formed at the both ends of the corrugations 120 and 130 where the bidirectional expandable member 140 is connected, at the “A” and “B” direction as shown in FIG. 5.

FIG. 8 is a perspective view illustrating an expandable metal membrane with orthogonally isotropic behavior according to a second embodiment of the present invention and FIG. 9 is a partially magnified sectional view illustrating an expandable metal membrane with orthogonally isotropic behavior according to a second embodiment of the present invention. As shown in FIG. 8 and FIG. 9, an expandable metal membrane with orthogonally isotropic behavior 200 according to a second embodiment includes corrugations 220 and 230 formed in the longitudinal direction and the transverse direction intersecting each other on a panel 210 made of metal, a bidirectional expandable member 240 at the intersection of the corrugations 220 and 230, in which the bidirectional expandable member 240 protrudes and is a dome shape.

The corrugations 220 and 230 are composed with first corrugations 220 formed in the longitudinal direction and second corrugations 230 formed in the transverse direction as described in the first embodiment.

The bidirectional expandable member 240 is connected to each of the front and back and the left and right of the first and the second corrugations 220 and 230 at the intersection of the first and the second corrugations 220 and 230. The bidirectional expandable member 240 is protruded upward and has a hemispherical dome shape having an appropriate radius. Accordingly, the bidirectional expandable member 240 allows the corrugations 220 and 230 to be expandable in the longitudinal direction and the transverse direction by having a dome shape to be flexible toward any direction.

The corrugations 220 and 230 include neck parts 221 and 231 which are narrower compared to other portions, at the portion where they are connected to the bidirectional expandable member 240 so that the corrugations 220 and 230 are easily expandable to the longitudinal direction and the transverse direction with the bidirectional expandable member 240 due to the expandability of the neck parts 221 and 231 provided by their folding and flattening.

The membrane may include clamping parts 250 at both sides of the bidirectional expandable member 240 to couple a clamping unit of a welding robot or a clamping unit of a guide rail to the membrane.

The clamping parts 250 are positioned to face each other between the portions connected to the corrugations 220 and 230 as shown in FIG. 8 and include indented part 251 for the clamping unit to clamp to the “A” and “B” directions.

The clamping unit may have a shape corresponding to the shape of the clamping part 250 to clamp the clamping part 250 easily.

As shown in FIG. 8, the expandable metal membrane with orthogonally isotropic behavior 200 according to a second embodiment of the present invention allows longitudinal and transverse expansion at intersection of the corrugations 220 and 230 by providing the dome-shaped bidirectional expandable member 240 expandable at the intersection of the corrugations 220 and 230 so that it reduces plane rigidity throughout the panel 210. Expandability in the longitudinal direction and the transverse direction of the panel 210 is kept by connecting the corrugations 220 and 230 to the bidirectional expandable member 240 to maintain continuity. Expandability is even improved and plane rigidity is significantly reduced by providing the neck parts 221 and 231 of the corrugations 220 and 230.

Further, a clamping unit of a welding robot or a transfer device may clamp the indented part 251, which are formed at the both sides of the bidirectional expandable member 240, at “A” and “B” directions as shown in FIG. 8.

FIG. 10 is a perspective view illustrating an expandable metal membrane having orthogonally isotropic behavior according to a third embodiment of the present invention. As shown in FIG. 10, an expandable metal membrane having orthogonally isotropic behavior 300 according to a third embodiment includes a plurality of corrugations 320 and 330 formed in the longitudinal direction and the transverse direction on a panel 310 made of metal, a bidirectional expandable member 340 at the intersection of the corrugations 320 and 330, in which the bidirectional expandable member 340 is protruded and has a cross shape and clamping parts 350 formed at both sides of the branching part 341 of the cross shape to couple a clamping unit of a welding robot or a clamping unit of a guide rail to a membrane.

The corrugations 320 and 330 are composed of first corrugations 320 formed in the longitudinal direction and second corrugations 330 formed in the transverse direction as described in the previous embodiments.

The bidirectional expandable member 340 is protruded as a cross shape at the intersection of the first and the second corrugations 320 and 330 and each of the first and the second corrugations 320 and 330 is connected smoothly to a branching part 341. When the first and the second corrugations 320 and 330 intersect each other, the branching part 341 forms a 45° with the first and the second corrugations 320 and 330. Expansion in the longitudinal direction and the transverse direction is provided by the deformation of the cross shape.

The side shape of the branching part 341 is a fan shape and each of the first and the second corrugations 320 and 330 is positioned near the vertex of the fan shape to be easily transformable against compression and tension.

The membrane may include clamping parts 350 at the branching part 341 of the bidirectional expandable member 340 to be clamped by a clamping unit of a welding robot or a clamping part of a transfer device which moves a metal membrane 300 along a guide rail.

The clamping parts 350 are formed at both sides of the branching part 341 by forming the bidirectional expandable member 340 to be more protruded than the corrugations 320 and 330 as shown in FIG. 10 and are formed for the clamping unit to clamp to the “A” and “B” directions.

The expandable metal membrane with orthogonally isotropic behavior 300 according to a third embodiment of the present invention allows longitudinal and transverse expansion at intersection of the corrugations 320 and 330 by providing the cross-shaped bidirectional expandable member 340 expandable at the intersection of the corrugations 320 and 330 so that it reduces plane rigidity throughout the panel 310. Expandability in the longitudinal direction and the transverse direction of the panel 310 is kept by connecting the corrugations 320 and 330 to the bidirectional expandable member 340 to maintain continuity. Deformation according to compression and tension is easily made, expandability is even improved, and plane rigidity is significantly reduced by providing the fan shaped side of the branching part 341 of the bidirectional expandable member 340 having the same radii from the arc-shaped edges to the corrugations 320 and 330.

Further, a clamping unit of a welding robot or a transfer device may clamp the clamping part 350, which are formed at the both sides of the branching part 341 of the bidirectional expandable member 340, at “A” and “B” directions as shown in FIG. 10.

As described above, each metal membrane is welded into a unit panel and the edge of each metal membrane is welded with the common edge of another adjacent metal membrane to keep a cargo warehouse air-tight, and ultra-low-temperature LNG is stored inside the cargo warehouse, so when the metal membrane contracts due to thermal deviation, the present invention reduces plane rigidity and, at the same time, equalizes plane rigidity of two intersecting directions.

While it has been described with reference to particular embodiments, it is to be appreciated that various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the embodiment herein, as defined by the appended claims and their equivalents. As such, many embodiments other than that set forth above can be found in the appended claims. 

1. A metal membrane with having orthogonally isotropic behavior in a metal membrane of a low-temperature-fluid storage tank having longitudinal and transverse corrugations which intersect each other, wherein: a bidirectional expandable member connected to each corrugation is formed so that the bidirectional expandable member is longitudinally and transversely expandable at an intersection of the corrugations; the bidirectional expandable member is protruded in a pyramid shape, and first caved grooves are formed at corners where lateral faces of the bidirectional expandable member are connected; second caved grooves are formed on a top part of the portion connected with the bidirectional expandable member in the corrugations; and clamping parts protruded to be clamped by a clamping unit are formed at both ends of the corrugations connected to the bidirectional expandable member.
 2. The metal membrane having orthogonally isotropic behavior of claim 1, wherein the upper part of the clamping part is more protruded than the bottom part of the clamping part.
 3. A metal membrane having orthogonally isotropic behavior in a metal membrane of a low-temperature-fluid storage tank having longitudinal and transverse corrugations which intersect each other, wherein: a bidirectional expandable member connected to each corrugation is formed so that the bidirectional expandable member is longitudinally and transversely expandable at an intersection of the corrugations; the bidirectional expandable member is protruded in a dome shape; a neck part is formed at the portion where the bidirectional expandable member is connected in the corrugations; and clamping parts indented to be clamped by a clamping unit are disposed at either sides of the bidirectional expandable member between portions where the bidirectional expandable member and the corrugation are connected.
 4. A metal membrane having orthogonally isotropic behavior in a metal membrane of a low-temperature-fluid storage tank having longitudinal and transverse corrugations which intersect each other, wherein: a bidirectional expandable member, protruded in a cross shape and connected to each corrugation between branching parts of the cross shape, is formed so that the bidirectional expandable member is longitudinally and transversely expandable at an intersection of the corrugations; and clamping parts are formed in such a way that the clamping parts are clamped by a clamping unit at either lateral face of the branching parts by having the bidirectional expandable member protrude over the corrugations.
 5. The metal membrane having orthogonally isotropic behavior of claim 4, wherein a side shape of the bidirectional expandable member is a fan shape. 